Walking after stroke is characterized by reduced gait speed and the presence of interlimb spatiotemporal asymmetry. These step length and stance time asymmetries can be energy inefficient, challenge balance control, increase the risk of falls and injury, and limit functional mobility. Current rehabilitation to improve gait is based on one of two competing motor learning strategies: minimizing or augmenting symmetry errors during training. Conventional rehabilitation often involves walking on a treadmill while therapists attempt to minimize symmetry errors during training. Although this approach can successfully improve gait speed, it does not produce long-term changes in symmetry. Conversely, augmenting or amplifying symmetry errors has been produced by walking on a split belt treadmill with the belts set at different fixed speeds. While this approach produced an 'after-effect' resulting in step length symmetry for short periods of time, with some evidence of long term learning in people with stroke, it had no influence on stance time asymmetry. We propose that patients need real-time proprioceptive feedback of symmetry errors so that they are actively engaged in the learning process. For this project, we developed and validated a novel, responsive, 'closed loop' control system, using a split-belt instrumented treadmill that continuously adjusts the difference in belt speeds to be proportional to the patient's current asymmetry. Using this system, we can either augment or minimize asymmetry on a step-by-step basis to determine which motor learning strategy produces the largest change in overground spatiotemporal symmetry. Using a randomized controlled design, 54 persons with chronic stroke who have stance time and/or step length asymmetry will receive 6 weeks (18 sessions) of locomotor training on a treadmill with either: 1) Asymmetry Augmentation, 2) Asymmetry Minimization, or 3) a Control condition (conventional treadmill training). We will measure spatiotemporal symmetry during overground walking using a GAITRite mat, at baseline, at 3 and 6 weeks of training, and at a 4-week follow-up to ascertain the cumulative effect of 6 weeks of training with each strategy. Additionally, we will demonstrate the effect of improved spatiotemporal symmetry on gait efficiency, balance, gait speed, endurance, quality of life, and physical activity in people with chronic stroke. Based on our preliminary data and the work of others, our central hypothesis is that the error augmentation strategy will produce the greatest motor learning, measured by overground gait symmetry after 6-weeks of locomotor training and at 4-week follow-up. Further, we expect that this innovative locomotor training approach will improve symmetric gait for people with stroke leading to increased gait efficiency, speed, and endurance, improved balance, greater physical activity, and better quality of life measures after training. PUBLIC HEALTH RELEVANCE: Many of the 780,000 people affected by stroke each year are left with slow, asymmetric walking patterns. The proposed project will evaluate the effectiveness of two competing motor learning approaches to restore symmetric gait for faster, more efficient, and safer walking.